Breastfeeding vent!

I didn’t breastfeed my first ds (dear son) who is now 10 yr old due to some medical complications when he was born and I felt like I missed that experience not having breastfed my baby...so I’ve been praying for another child and all I wish is to be able to experience the wonderful of breastfeeding so fast forward I got pregnant after 10 yrs of trying and finally blessed with a healthy baby boy....I’m exclusive breastfeed my now 9 months old and here’s the problem...I don’t know why my son is small 1% percentile he’s only 15 lbs and 23 inches which very short base in the chart. We did blood draw to check if we are missing anything and everything is negative thyroid is good and he is healthy he does also he ears very good and like every kind of food. I’ve tried supplementing with formula but he just won’t drink it and I know my supply is slowly decreasing. I’m frustrated just because no one had told me I should introduce the bottle earlier and I’m frustrated because I don’t think my milk has enough fat! I also tried every kind of bottle available you name...and he just won’t drink it. His dad or my mom tried giving the bottle to him and he still refused. Ahhhh I just wanted to vent this out!